1. Field of the Invention
This invention relates generally to insecticidal compositions containing nematodes which are useful for the biological control of noxious insects.
2. Description of Related Art
Insect nematodes (Steinernematidae, Heterorhabditidae, Mermithidae) have been shown to be highly effective bioinsecticides (Poinar, "Nematodes for Biological Control of Insects" CRC Press, Inc., Boca Raton, Fla., 1979). However, insect nematodes require moist conditions to survive and function. When nematodes are dried they lose activity rapidly; subsequent rehydration fails to restore the lost activity. One method of preserving nematodes in a moist environment is via the microencapsulation processes of U.S. Pat. Nos. 4,615,883, 4,701,326, and 4,753,799. This art microencapsulates the nematodes in calcium alginate. The alginate microcapsules, however, have several drawbacks. They are fairly large and rigid and consequently are not appealing to insects as well as being out of the chewing range of smaller insects. Additionally, the ability of the alginate microcapsules to maintain moisture conditions conducive to survival of the nematodes has also been questioned (Dunkle and Shasha, Environ. Entomol., Vol. 17,120-126, 1988). To reduce the rate of desiccation, others have used water thickeners, mineral oil, or surfactants. See, for example, U.S. Pat. No. 4,178,366. With insect nematodes most of these approaches are ineffective in preserving the moisture content and consequently the biological activity. Some have adverse effects on biological activity or repel the target insects, thereby making them ineffective for their intended purpose.
Another factor greatly limiting the effective use of nematodes for biological control of insects is the inability of the nematodes to survive for an extended period of time at high temperatures. High temperatures are frequently encountered in the field during summer months and in unregulated storage warehouses.
U.S. Pat. No. 3,271,243 (Cords et al.) discloses an oil-water suspension of Bacillus thuringiensis, including vegetable, animal or mineral oils, such as corn oil. The resulting insecticide is dependent on pH and salt concentration.
U.S. Pat. No. 4,859,377 (Shasha et al.) discloses the encapsulation of corn oil and entomopathogens in starch. Encapsulation of Bacillus thuringiensis and of nuclear polyhedrosis virus is demonstrated in the presence of corn oil.
U.S. Pat. No. 4,178,366 (Bedding) discloses an oil suspension of nematodes. The harvested, unprotected nematodes are stored in oil and/or wax. The patent also indicates that nematodes may be kept alive when suspended in water through which air is bubbled at a rate sufficient to insure that the nematodes are subject to some degree of agitation.
U.S. Pat. No. 4,765,275 (Yukawa et al.) discloses an improved method for the storage and transport of nematodes. This patent recommends the storage of nematodes under substantially anaerobic conditions as a means for prolonging their viability.
It is an object of this invention to provide a formulation for keeping nematodes viable.
Another object of this invention to provide stable nematode formulations that can be stored at high temperatures without appreciable loss of activity. Preferably the nematode formulation should be stable for months at 32.degree. C. or for several weeks at 37.degree. C.
Another object of the invention is to provide a means to maintain the nematodes in a moist environment. Preferably, the nematodes may be maintained in a moist environment for an extended period of time even at high temperatures.
Still a further object is to provide means to attract insects to the formulations and, once attracted, to induce the insects to consume the moist and viable nematodes.